As compared to other display devices such as liquid crystal display (LCD) devices, the organic light emitting diode (OLED) display devices are self-emitting apparatuses that do not require a backlight. Having the advantages of fast response, low power consumption, a wider viewing angle, high brightness, more vivid color rendering, thinner and lighter, they have found a wide range of applications in display field.
Light emission in an OLED device are driven by current. To achieve a display with uniform brightness, a stable current at each pixel unit is essential. Various factors, such as a defective manufacturing process and aging components, could result in shift of threshold voltage of driving thin film transistor in an array substrate from the standard value. The shift of threshold voltage in turn results in variation of the current applied to each pixel, leading to non-uniform display of OLED.